It is common practice in reciprocating piston compressors to drive a piston push rod by a rotating eccentric cam. The remote end of the piston push rod is held in contact with the surface of the cam by the force of a compression return spring. Thus, the cam drives the piston push rod to cause the reciprocating piston to move through a compression stroke of the spring force. Upon completion of the compression stroke, the reciprocating piston is moved by the force of the return spring through a suction stroke.
When such a reciprocating piston-type of compressor is used in a compressed air generating plant, it is necessary to limit the upper pressure level. That is, when the pressure is raised to the appropriate value, it is advisable to unload the reciprocating piston compressor. Further, after the achievement of the desired pressure in the compressed air reservoir, it is highly detrimental to reciprocate the piston under load. In the past, an appropriate pressure regulating valve sensed the compressed air produced by the reciprocating piston compressor after the achievement of the desired pressure, and the pressure was vented into the atmosphere. However, the reciprocating piston compressor still continues to run in an unload condition and is still subject to some degree of wear. Therefore, it would be beneficial to completely disconnect or stop the reciprocating piston of the compressor during periods of no demand.